1. Field of the Invention
The present invention relates to an inkjet printhead. More particularly, the present invention relates to an inkjet printhead having a cantilever actuator that can reduce the volume of an ink chamber and increase the number of channels per inch (CPI).
2. Description of the Related Art
In general, inkjet printheads are devices for printing a predetermined color image by ejecting a small volume ink droplet at a desired position on a print medium, e.g., a sheet of paper or a fabric. Inkjet printheads are largely categorized into two types, depending on the ink ejection mechanism: thermal inkjet printheads and piezoelectric inkjet printheads.
The ink ejection mechanism in the thermal inkjet printheads, which rely on heated ink to provide a driving force, will now be briefly described. Generally, a thermal inkjet printhead relies on heating ink in an ink-filled chamber to generate bubbles, which in turn force ink out of the inkjet printhead. In greater detail, a current pulse flows through a heater formed of a resistance heating material to generate heat in the heater and in ink adjacent to the heater, such that the ink is rapidly heated. When the ink is boiled, bubbles are generated in the ink and expand, thereby applying pressure to the inside of the ink chamber. As a result, ink in the vicinity of a nozzle is ejected from the ink chamber as droplets exiting through the nozzle. Since such a thermal inkjet printhead generates bubbles by heating ink until the ink reaches a temperature of hundreds of degrees Celsius, a significant amount of energy is consumed and a high thermal stress is applied on the printhead. Further, a significant amount of time is required to cool the heated ink, limiting the ability to increase the driving frequency.
In contrast to thermal inkjet printheads, piezoelectric inkjet printheads eject ink using a piezoelectric element as a driving force. In such a printhead, the piezoelectric element deforms and this deformation is transferred through a wall of the ink chamber to apply pressure to the ink.
A conventional piezoelectric inkjet printhead is illustrated in FIGS. 1 and 2. Referring to FIGS. 1 and 2, a manifold 13 coupled to a restrictor 12 and an ink chamber 11, which together constitute an ink channel, may be formed on a channel plate 10. Of course, a typical inkjet printhead may have a number of ink channels thereon. A nozzle 22, arranged to correspond to the ink chamber 11, may be formed on a nozzle plate 20. A piezoelectric actuator 30 may be disposed on the channel plate 10.
The manifold 13 forms a path through which ink is introduced from an ink reservoir (not shown) and supplied to ink chamber 11. The restrictor 12 forms a path through which ink is introduced from the manifold 13 to the ink chamber 11. The ink chamber 11, in which ink to be ejected is contained, is arranged alongside the manifold 13. Where a number of ink channels are provided, ink chambers may be arranged along both sides of the manifold 13. The volume of the ink chamber 11 is changed by driving the piezoelectric actuator 30 to produce a pressure change for ink ejection and/or introduction. To this end, a portion of the ink chamber, e.g., a portion of the channel plate 10 forming an upper wall, i.e., a ceiling wall, of the ink chamber 11, may act as a vibration plate 14 that is deformed by the piezoelectric actuator 30.
In the operation of the conventional piezoelectric inkjet printhead constructed as described above, when the vibration plate 14 is deformed by the driving of the piezoelectric actuator 30, the volume of the ink chamber 11 is reduced. Accordingly, an internal pressure of the ink chamber 11 is changed such that ink contained in the ink chamber 11 is outwardly ejected through the nozzle 22. Subsequently, if the vibration plate 14 returns to its original state, due to the driving of the piezoelectric actuator 30, the volume of the ink chamber 11 is increased, the internal pressure of the ink chamber 11 is accordingly changed and ink is introduced from the manifold 13 through the restrictor 12 to the ink chamber 11.
When an image is printed using the conventional piezoelectric inkjet printhead having the above structure, the resolution of the image is directly affected by the number of nozzles per inch. Herein, a number of channels per inch (CPI) generally indicates the number of nozzles per inch, and a number of dots per inch (DPI) is generally a measure of the resolution of the printed image.
In the conventional piezoelectric inkjet printhead illustrated in FIGS. 1 and 2, the volume of ink droplets ejected through the nozzle 22 is greatly affected by the displacement of the vibration plate 14. That is, a large displacement of the vibration plate 14 results in large ink droplets, and a lesser displacement of the vibration plate 14 results in smaller ink droplets. The displacement of the vibration plate 14 is dependent on the area of the vibration plate 14, and the area of the vibration plate 14 is dependent on the volume of the ink chamber 11. That is, since the vibration plate 14 may constitute an upper wall of the ink chamber 11, the dimensions of the vibration plate 14 correlate directly with an area of the upper wall of the ink chamber 11 and, accordingly, with the volume of the ink chamber 11.
In the conventional inkjet printhead, when the vibration plate 14 is deformed by driving the piezoelectric actuator 30, ink is ejected through the nozzle 22 and also flows back toward the manifold 13 via the restrictor 12. Accordingly, to eject ink droplets of a predetermined volume, the displacement of the vibration plate 14 needs to take into account the amount of ink backflow. Accordingly, the area of the vibration plate 14, and thus and the area of the ink chamber 11, may need to be increased in order to maintain the desired volume of ink ejected from the nozzle 22.
Generally, the number of CPI of the piezoelectric inkjet printhead is in inverse proportion to a distance DN between adjacent nozzles 22. Thus, to increase the number of CPI of the printhead, the distance DN between the adjacent nozzles 22 should be reduced. However, the conventional piezoelectric inkjet printhead having the structure described above has limitations in reducing the distance DN between the adjacent nozzles 22 for the previously mentioned reasons. In particular, reducing the distance DN may affect the area of the ink chamber 11 and the area of the vibration plate 14, thereby reducing the volume of ink that can be ejected.
Another aspect of the conventional inkjet printhead is that it may be employed to print an image on a sheet of paper or other print medium by causing it to reciprocate in a direction orthogonal to a feed direction of the sheet, i.e., where the sheet is fed lengthwise into the printer, the inkjet printhead may be reciprocated in a width direction of the sheet.
Accordingly, the need to reciprocate the conventional inkjet printhead may result in a slow printing speed.
Inkjet printheads having a length equal to the width of a sheet of paper have been developed to increase printing speed. Such a printhead may have a plurality of nozzles that are arrayed in a width direction of the sheet of paper to print an image on the sheet at high speed without reciprocation in the width direction of the sheet. An inkjet printhead having this structure is generally called a page-wide inkjet printhead.
However, in order to print an image with sufficiently high resolution, without any reciprocation in a width direction of the sheet of paper, the number of CPI needs to be equal to the number of DPI of an image. Since the conventional piezoelectric inkjet printhead has structural limitations in increasing the number of CPI, as described above, it may be difficult to have the number of CPI equal the number of DPI of the image. Accordingly, to satisfy the demands for images with high resolution while maintaining or improving print speed, further efforts are needed to increase the number of CPI of a printhead.